The foundry art has three general types of processes for producing castings. In one type of process, the half sections of a pattern are accurately secured to flat surfaces and usually to the opposite sides of a flat pattern plate. A foundry flask that is a rectangularly shaped box having open top and bottom sides is accurately positioned against one side of the pattern plate, and a foundry sand containing a clay or other type of binder is tamped around the pattern section. The flask and pattern are inverted and the pattern plate lifted from the top of the flask to expose the surface of the sand having a cavity therein conforming to the pattern section. Thereafter the sand is dried and its binder hardened and the process is repeated for the other half section of the pattern. The two flasks having the mold cavities therein, are accurately booked or aligned, as will later be explained, to provide the total cavity into which molten metal is poured.
In another type of process which makes what are called "shell molds", the two half pattern sections are made of metal and each is accurately installed upon the flat surface of a metal plate or plates. This plate is made to be a part of the pattern heating box of a large machine called a shell mold forming machine. Such a machine also includes a rectangularly shaped sand tank which holds resin coated sand and which must be accurately positioned on top of the pattern heating box containing the pattern and pattern plate. The pattern heating box containing the pattern section is placed on top of the sand tank, and the sand tank and heating box inverted so that binder coated sand in the sand tank falls down on top of the heating box and pattern section. The box and pattern section are heated so that the resin coated sand adjacent the heated surfaces of the pattern section and box become hardened to a depth of approximately one half inch to provide a "shell" of sand and cured resin. The said tank and heating box are inverted to allow the loose sand to fall back down into the sand tank, and the "shell" containing an accurate impression of the pattern section is removed from the pattern plate. This process is repeated with respect to the pattern plate containing the other half section of the pattern, and the two "shells" are thereafter cemented together to form the total cavity that is to be filled with the molten metal. The booked and cemented "shells" are embedded in sand or metal shot to a sufficient depth to withstand the hydrostatic head of the molten metal.
The third type of process commonly used is called the "hot box process" which is similar to the "shell molding" process but differs principally therefrom in that the box surrounding the pattern is heated, and the resin coated sand is introduced into the heated box from a separate container. In the "hot box process", the resin surrounding the pattern is cured in depth to form a finished cured mold.
In the processes above described, it is essential that the two half sections of the pattern be accurately located on pattern plates, and that these pattern plates be accurately located relative to the flasks, hot boxes, etc. in order that the molded sand will have side or other reference surfaces which can be easily aligned with respect to each other.
In the first described process, it is necessary to accurately register the pattern plate and flasks and thereafter accurately register the flasks containing the half mold sections. In the second or third processes above described, it is necessary to accurately position or register the pattern plate with the sand tank, or hot box, used to form the molds. In any of the processes given above, the means which has been found most convenient for performing the necessary alignment, comprises the use of a plurality of cooperating pins and bushings, the pins of which are received in accurate internal guide surfaces of the bushings. In those instances where large castings are to be made, it is relatively impossible to obtain equal thermal expansion of all mated metal parts of the equipment when heated to cure the resin of the coated sand. The means customarily used to accommodate the difference in thermal expansion is the utilization of at least one bushing containing a round opening which tightly engages the pin, while the bushings which are positioned remotely therefrom, contain elongated openings having internal parallel guide surfaces that are oriented in the direction of thermal expansion. The elongated bushings of the prior art have been of two general types: the first of which has external threads which extend through the flask, or the hot box, as the case may be, and which are secured in place by a nut on the back side of the member in which it is installed. Whenever one of these bushings becomes damaged, or the guide pin becomes broken, it is necessary to take the flask, the shell molding machine, or the hot box machine, as the case may be, out of operation and drill or "fish out" the broken pin or bushing.
The most commonly used type of bushing has been one with plain cylindrical side surfaces, which surfaces are provided with an interference fit relative to the receiving openings which are made in the flasks, pattern heating boxes, hot boxes, etc. in which they are to be installed. The bushings are installed with its internal oblong opening "eye-balled" in the direction of thermal expansion. The bushing is thereafter, pressed into the receiving opening. Some rotation of the bushing usually always takes place while it is being pressed down into the receiving opening, so that the installed bushing is not properly aligned, and undue wear of the guide pins and bushings occurs.
A further difficulty with the prior art guide bushings and pins has occurred by reason of the continuing heating up and cooling down of the equipment in which the pins and bushings are installed. If this heating up and cooling down is not accompanied by condensation, the bushing may eventually loosen up in its receiving opening. In most instances, however, some condensation is present, and in this instance, the bushings and pins, and particularly the pressed in bushings and pins become frozen into the equipment into which they are installed, particularly where the equipment is cast aluminum. The removal of the bushings or pins is made difficult because they are hardened to withstand the abrasion of the foundry sand and are, substantially, nonmachinable. In many instances the equipment must be removed to a machine shop where the best available equipment and techniques are available for "fishing" the bushing out of the equipment.
Pins and bushings of the press fit type are usually made in an original equipment size, plus at least two oversizes. Each oversize pin or bushing is used to replace the next smaller size pin or bushing. Not only is the removal of the pins and bushings difficult and costly, but the warehousing, selecting and installation of the replacement items is expensive.
An object of the present invention, therefore, is the provision of a new and improved bushing the guide surfaces of which can be more accurately positioned in the equipment in which the bushing is installed than can the prior art bushings.
A further object of the present invention is the provision of a new and improved guide bushing which can be easily removed and new guide surfaces installed without the removal of the equipment in which the bushing is installed to machine shops, etc.
Further objects and advantages will become apparent to those skilled in the art from the drawings and following description of the preferred embodiments.